Molten metals and plastics which are used for casting components have in the temperature range of the molten state a very low viscosity. This characteristic results in that even smallest gaps and cavities, for example in an insert or in a casting mold, are infiltrated at the casting of these molten materials. This is especially the case at pressure-supported casting methods such as, for example, at the aluminum die-casting or at injection molding methods for plastics. During the molding or over molding of inserts, such as threaded inserts, with molten metal or with liquid plastics, the risk is thus that the liquid materials are infiltrated in the insert, for example the thread of the above-mentioned threaded insert, and thereby affect the later function of the insert. For subsequently introducing inner threads at cast components, for example of metal or plastic, there is generally the possibility that the inner threads are included in a subsequent process step by cutting production methods. At the subsequent including of the thread into the cast material, it may come to the exposure of porosities being present in the cast material, which weaken the strength of the thread and lead to defective work.
A possibility for creating inner threads during the casting processes is the usage of so-called collapsible cores. This technique comes from the plastic injection molding and could be transferred to the die-casting of zinc. The collapsible cores have the structure to be reproduced radially on the core surface. By a segmentation of the core, it is possible to “fold” the collapsible core after solidification of the molten material and to demold the component in this way.
In metal die-casting as well as in sand or permanent mold casting, inner threads may also be created by the subsequent introducing of threaded sleeves. Established are for example self-cutting threaded sleeves of annealed steel which may be screwed directly into cored bores. Also, wire thread inserts have a wide usage in which a female thread is cut into a cored bore, in which subsequently the wire thread insert may be screwed in. The advantages are a secure side or flank contact over the complete length of the thread and an increase of the strength of the complete connection by 25-30%. These advantages can be used constructively with respect to small installation depths and small thread diameters.
The molding of inserts, as for example metallic inserts, in molten metal or molten plastics is known and described under the term “material compounds” or “compound casting”. In engine pistons of cast aluminum for example piston ring seats from an iron nickel alloy are molded. The molding of steel-based threaded inserts in aluminum casting has the target to achieve a higher loadability as it is provided by a thread cut into aluminum. The fit of the molded insert takes place by a form and force-fit bond which is achieved by shrinking the solidifying cast metal.
The patent document EP 1 046 446 B1 describes a casting technically produced metal cast part with directly molded gapless wound wire coil. The wire coil acts as a thread in the cast part and is freely accessible from both sides. The casting technically integration is such that a mold half of a two-part casting tool has a fixed cylindrical core pin onto which the two-sided open, gapless wire winding (similar to a spiral) with tightly fitting windings is placed. Subsequently, the mold tool is closed and a cylindrical core pin is inserted into the wire winding also from the other side. Both core pins are slightly conically widened to the end of the windings so that they slightly stretch the wire winding upon closing of the casting tool and thus ensure a tight pressing of the core pin onto the wire winding. Nevertheless, an entering of molten metal on the face side during the casting has proven to be disadvantageous as wire threads are blocked thereby.
Furthermore, with the technical solution approach described here, only a continuous, two-sided open thread can be created in a cast part. However, no threaded blind hole can be produced which is open only on one side. Furthermore, no approach is described in order to prevent in a process-reliable manner the entering of molten metal into the exposed thread of the wire thread insert, thus at the entrance and the exit of the wire thread insert.
In U.S. Pat. No. 3,945,070, a method for molding a wire thread insert into molten metal is described. During the casting method, the wire thread insert is arranged on a pin. The solidifying of the molten metal after the casting process leads to a material shrinkage which changes the thread pitch of the wire thread insert. This material change is deliberately included in the thread pitch of the wire thread insert so that after solidifying of the cast part the desired pitch of the thread results. U.S. Pat. No. 3,945,070 provides no information about how the entering of low viscous molten material can be prevented laterally and on the face side.
In U.S. Pat. No. 3,112,540, the production of a blind hole with wire thread insert in a cast part is disclosed. To this end, the wire thread insert is screwed onto a holding core with thread and is subsequently molded into the molten metal. For achieving an increased strength of the wire thread insert in the cured cast part, several threads at the closed side of the blind hole are molded into the molten metal.
In U.S. Pat. No. 2,672,070, a wire thread insert is molded into a cast part without that the liquid material of the cast part can enter the interior of the wire thread insert in a radial direction. For this purpose, the cross-section of adjacent windings are formed such that they abut each other like a labyrinth seal. Further, in the course of this labyrinth seal, a cavity is provided in which possibly infiltrated molten material can solidify. This solidified molten material blocks then additionally to the labyrinth seal the entering of the liquid material into the interior of the wire thread insert. Besides the elaborate production of such wire thread inserts, the here described solution concept is not described for metal casting methods.
DE 10 2009 048 160 A1 describes a wire thread insert for the molding into a cast part of molten metal or molten plastic having at least at an axial face side a wound flange. By means of this wire thread insert, through holes as well as blind holes are producible in a cast part. For preventing a radial entering of plastic or molten metal into the interior of the wire thread insert, adjacent windings abut each other two-dimensionally like a labyrinth seal or the radial outer side of the wire thread insert is sealed by a suitable and externally applied seal mass.
The description of the prior art shows that, especially at cast components of non-ferrous metal, the usage of thread inserts has technical advantages, primarily with respect to the mechanical loadability of the thread. To this end, methods exist for subsequently including thread inserts by means of mechanically processing the cast part (for example at the usage of wire thread inserts), the two or multi-step process of which is disadvantageous and economically elaborate. A further approach is the direct molding of thread inserts in the metal casting process. However, there are no technical descriptions for the process reliable preventing of the entering of molten metal or molten plastic in the thread of an insert during molding or over molding of the molten material.
Also, there is no indication in the prior art how the molten metal or molten plastic which is introduced with high velocity into the casting mold affects the threaded insert in the casting mold. The same applies to the consideration of material shrinkage processes during cooling of the molten material in the casting mold. If a material shrinkage within the cooling cast component should take place differently with respect to the possible spatial directions, mechanical tension states and failure states result which affect the integrity of the cast component. It is therefore disadvantageous in the prior art not to identify the possibility of such states and to take no counter measures.
A direct integration of inserts, as for example wire thread inserts, in the casting process offers economical and technical advantages, primarily due to the cost-effective manufacturing of the thread insert in the wire winding method. However, there is especially upon usage of wire thread inserts the risk that molten material cannot only infiltrate the thread via the one or two, respectively, open face sides of the thread insert but also via the individual threads merely lying tightly against each other by pressing. This aspect is primarily critical at the molding or over molding of wire thread inserts in pressure supported metal casting methods and plastic injection molding methods. A technical description of a solution for this does not exist according to the present prior art.
It is therefore the object of at least certain implementations of the present invention to provide a casting technical integration of inserts, especially of wire thread inserts, during the casting processes by means of molten metal or molten plastic, wherein a flowing of molten metal or molten plastic into the interior of the inserts is process reliably prevented. Further, it is an object of at least certain implementations of the present invention to consider shrinkage processes in the cast material and to counteract the loads resulting therefrom in the cast component.